Alkalinization of acid whey by means of electrodialysis with bipolar membranes and analysis of induced membrane fouling

Journal Pre-proof Alkalinization of acid whey by means of electrodialysis with bipolar membranes and analysis of induced membrane fouling Vitalii Kravtsov, Irina Kulikova, Sergey Mikhaylin, Laurent Bazinet PII:

S0260-8774(19)30534-5

DOI:

https://doi.org/10.1016/j.jfoodeng.2019.109891

Reference:

JFOE 109891

To appear in:

Journal of Food Engineering

Received Date: 26 March 2019 Revised Date:

18 October 2019

Accepted Date: 20 December 2019

Please cite this article as: Kravtsov, V., Kulikova, I., Mikhaylin, S., Bazinet, L., Alkalinization of acid whey by means of electrodialysis with bipolar membranes and analysis of induced membrane fouling, Journal of Food Engineering (2020), doi: https://doi.org/10.1016/j.jfoodeng.2019.109891. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Alkalinization of acid whey by means of electrodialysis with bipolar membranes and analysis of induced membrane fouling

1 2 3

Vitalii Kravtsova¹, Irina Kulikovaa, Sergey Mikhaylinb, c, Laurent Bazinetb, c,

4 5 6

a

Chair of Applied Biotechnology, Institute of Life Sciences, North-Caucasus Federal University, 1 Pushkin St., Stavropol 355009, Russia

7 8

b

Institute of Nutraceuticals and Functional Foods, Dairy Research Center, and Department of Food Sciences, Université Laval, Québec, QC, Canada G1V 0A6

9 10

c

Laboratory of Food Processing and ElectroMembrane Processes, Université Laval, Québec, QC, Canada G1V 0A6

11 12

¹Corresponding author. [email protected]

13

Abstract

14

An issue of acid whey processing, well known in the dairy industry, is its high amount of lactic

15

acid, a key feature that hampers acid whey industrial utilization. As a result, dried products of

16

acid whey treatment possess a number of undesirable properties such as elevated acidity,

17

hygroscopicity and caking. In the present study, electrodialysis with bipolar membranes (EDBM)

18

was used to alkalinize acid whey at laboratory scale. Two alternative configurations of

19

electrodialysis cells were designed, where the whey stream was directly connected to the bipolar

20

membrane generating hydroxide ions. pH of acid whey was raised up to 6.5. The above said pH

21

adjustment corresponded to 25% lactic acid removal rate and 24–34% demineralization rate. The

22

operation of EDBM, although efficient, induced fouling on the anion-exchange side of bipolar

23

membranes after acid whey alkalinization. A complex analysis of membranes after whey

24

processing was conducted. The analysis of whey precipitate and membrane fouling revealed 13

25

and 7% protein content in respective dried samples. Membrane fouling displayed minor protein

26

content; thus, mineral fraction was likely to be dominant in the fouling matter.

27 28 29 30

Keywords Acid whey; lactic acid; electrodialysis; bipolar membranes; fouling; alkalinization

31

1. Introduction

32

A number of approaches was developed to utilize whey in food products. Whey is widely

33

applied as a supplement in different branches of food industry due to the high nutritional value of

34

its main components (Królczyk et al., 2016). Moreover, there is a series of whey-derived

35

condensed and concentrated products, e.g. protein concentrates, isolates and hydrolysates,

36

demineralized powders (Duke and Vasiljevic, 2015; Kilara, 2016). Acid whey, a by-product of

37

casein, strained yogurts and cottage cheese manufacturing, contributes significantly to the

38

worldwide whey production. The content of proteins and carbohydrates is similar in sweet and

39

acid whey (Nishanthi et al., 2017b); however, some of the chemical properties of acid whey

40

became a stumbling block, hampering its treatment and utilization (Bédas et al., 2017a;

41

Chandrapala et al., 2017, 2016a; Chen et al., 2016; Nishanthi et al., 2017a, 2017b).The major

42

issue impeding acid whey treatment is its high lactic acid content, which prevents proper lactose

43

crystallization. Also, the hygroscopicity of lactic acid leads to the increase in whey powder

44

moisture absorption, resulting in the product storability and yield (Chandrapala et al., 2017,

45

2016a, 2016c; Chandrapala and Vasiljevic, 2017; Chen et al., 2016). Reduction of lactic acid

46

content in whey may be achieved by electrodialysis (Chen et al., 2016; Dufton et al., 2018).

47

Although electrodialysis does not provide a selective removal of lactic acid, it is still applicable,

48

as the desalination of whey is a regular and favourable process in terms of whey concentrates

49

technology (Zadow, 1992).

50

Clearly, high acidity of whey demands partial or full neutralization prior to its addition to food

51

products as a supplement in order to prevent alteration of organoleptic and physicochemical

52

properties. Thus, an extra technological operation of pH correction is introduced, making the

53

technology more complicated and more expensive. Conventionally, the alkali reagent is added

54

to adjust the pH of whey. However, this approach influences the ionic composition of whey;

55

also, the addition of basifying compounds such as sodium or potassium hydroxide counteracts

56

the desalination and makes the technology even more inefficient. An alternative way to adjust

57

pH of acid whey is electrodialysis with bipolar membranes (EDBM). There are numerous studies

58

dedicated to EDBM application in food industry. There are reports on proteins separation and

59

purification, juices neutralization, enzymatic inhibition in food products by means of EDBM,

60

e.g. (Mier et al., 2008; Rozoy et al., 2015; Tronc et al., 1997). Recently, Dufton et al.

61

investigated deacidification of acid whey by means of ED with conventional stack configuration

62

and a three-compartment stack configuration comprising bipolar membranes (Dufton et al.,

63

2018). The latter stack was designed to recover lactate from acid whey and protonate it with

64

electrogenerated H+ so that the lactic acid could form. Merkel et al. reported successful

65

neutralization of acid whey nanofiltration retentate up to pH 6.2 using different ED stack

66

configurations with bipolar membranes in contact with whey stream (Merkel et al., 2018).

67

Hydroxide ions produced by bipolar membranes were utilized for pH correction in the feed. In

68

contrast to the mentioned papers, present work is focused on the study of membrane fouling,

69

especially one caused by the direct contact of acid whey stream with the anion-exchange surface

70

of BPM. moreover, a special attention was paid to the protein contribution to membrane fouling

71

and bulk precipitation induced by EDBM processing. The protein content in the fouling matter

72

and bulk precipitate were quantified in Supplementary materials section.

73

The aim of the present work was to evaluate the performance of acid whey alkalinization using

74

two alternative EDBM cell configurations in terms of lactic acid removal, demineralization rate

75

and energy efficiency. The membrane fouling induced by EDBM of acid whey was also

76

investigated.

77 78

2. Materials and methods

79

2.1 Chemicals, raw materials, and membranes

80

The raw acid whey was obtained from a dairy processing plant owned by Parmalat-Canada

81

(Victoriaville, Quebec, Canada). The acid whey samples were transported at 4 °C from the plant

82

and then stored at –30 °C. Samples were thawed at 4 °C before each experiment. The

83

composition of the acid whey is described in Table 1 and was found to be consistent with that

84

reported in the literature (Bédas et al., 2017b; Chen et al., 2016; Panesar et al., 2007; Saffari and

85

Langrish, 2014).

86

NaNO3, KCl were of ACS purity (VWR International, Mississauga, Canada). Ion-exchange

87

membranes used in the study were Neosepta anion-exchange AMX, cation-exchange CMX and

88

bipolar BP-1 (Tokuyama Corporation, Tokyo, Japan).

89

2.2 Electrodialysis cell

90

The electrodialysis cell was a laboratory-scale cell (Model MP, 100 cm2 effective surface,

91

ElectroCell Systems AB Company, Täby, Sweden). The cell included a 316 stainless steel

92

cathode and dimensionally-stable anode. The electrodialysis cell included three looped flows:

93

800 mL of diluate (acid whey), 800 mL of concentrate (0.5 mS/cm KCl) and 1 L of electrode

94

solution (20 mS/cm NaNO3). Electrode solution and concentrate were obtained by dissolving

95

reagents in main water (0.2–0.3 mS/cm). The flow rates were 400 mL/min for diluate and

96

concentrate and 900 mL/min for electrode solution. The electrodialysis treatments were carried

97

out at room temperature (22 ± 2 °C).

98 99 100

2.3 Protocol Two cell configurations were tested in the present study (Fig. 1). Cell configuration 1 included two CEMs, one AEM and one BPM membrane and was capable to perform alkalinization of

101

whey stream and removal of anionic species therefrom. The CEM adjacent to anode was

102

introduced to prevent migration of electrogenerated OH– ions from acid whey compartment to

103

anolyte; another CEM was added to maintain electrolyte concentration in the electrode solution

104

relatively constant. Cell configuration 2 included two AEMs and one BPM and corresponded to

105

the elementary cell for simultaneous BPM-assisted alkalinization and removal of anionic species.

106

EDBM was conducted in a batch mode at a constant voltage of 10 V, generated by a power

107

supply, (Keithley 2200-60-2, Textronix, Inc., Beaverton, USA). The initial pH value of acid

108

whey was 4.3 ± 0.1; EDBM process was stopped after whey pH reached 6.5. Prior to cell

109

disassembling at the end of the process, the cell was rinsed with water for 10 min at flow rates

110

equal to that during the EDBM process. The experiments were carried out in triplicate. pH

111

values, conductivity, temperature of solutions and electric current through the cell were

112

registered during the treatment. After the EDBM, photographs of fouled membranes and spacers

113

were taken. Membrane thickness, conductivity and ash content were analyzed in order to

114

characterize the significance of fouling induced by the treatment. Whey after EDBM was

115

lyophilized to undergo protein and ash content analysis and mineral concentration determination.

116

HPLC of whey and KCl solutions were carried out to determine lactic acid removal rate.

117

2.4 Analyses

118

2.4.1 pH of the solutions

119

The pH of acid whey, KCl solution and electrode solution was measured using a SP20

120

sympHony portable meter (VWR International, Mississauga, Canada).

121

2.4.2 Conductivity of the solutions

122

The conductivity of acid whey, KCl solution and electrode solution was measured with

123

a YSI 3100 conductivity meter (Yellow Springs Instrument, Yellow Springs, USA) equipped

124

with a conductivity cell 3252 (cell constant K = 1/cm).

125

2.4.3 Global resistance of ED cell

126

The cell global resistance was calculated by Ohm’s law using the recorded values of current:

127

R=

128

U (in volt) is the potential difference between electrodes, I (in A) is the electric current.

129

U , I

2.4.4 Energy consumption

130

The following expression was used to calculate the specific energy consumption of EDBM to

131

alkalinize 1 kg of acid whey:

132

U Esp. = ∫ I dτ , m0

Τ

133

U is the voltage applied to electrodes (V), m is the mass of treated whey (kg), I is the instant

134

current value (A), τ is time (argument), Τ is total duration of the electrodialysis (s). To obtain

135

instant values of electric current, the polynomial approximating function was calculated: 6

I = ∑ ciτ i , 136 137 138

i =0

ci are constant coefficients. 2.4.5 Number of electrogenerated ions

139

The amount (mol l–1 h–1) of electrogenerated H+ and OH– ions was estimated using Faraday’s

140

law for electrolysis (Bazinet et al., 2000):

141

nEG (OH − ) = nEG (H + ) =

142

η is current efficiency coefficient (0.85 (Lin Teng Shee and Bazinet, 2009)), Q is total charge of

143

electrogenerated ion species (C), F is Faraday’s number (C mol−1), m is mass of processed whey

144

(kg), τ is total EDBM duration (h).

145

ηQ , Fmτ

2.4.6 Ash content

146

The ash content of membranes was determined according to the AOAC method no. 945–46.

147

Membranes were dried overnight at 60 °C in a convection oven (Model 414005-112, VWR

148

International, Mississauga, Canada). Approximately 0.1 g of membrane sample was added to a

149

calcined cooled crucible, and the mass was recorded. The sample was then heated at 550 °C for

150

16 h in a muffle oven and weighted again after cooling at room temperature. To determine the

151

ash content in whey powder, approximately 0.5 g of a lyophilized whey sample was placed to a

152

calcined crucible and ashed in the same conditions. Moisture content in lyophilized whey

153

samples was determined in accordance with AOAC method no. 927.05. A sample was placed in

154

metal container and dried at 100 °C in the Isotemp Vacuum Oven Model 280A (Fisher

155

Scientific, Pittsburgh, USA) for 5 h. Moisture content was calculated based on the mass loss of

156

the sample after drying.

157

2.4.7 Inductively coupled plasma optical emission spectroscopy (ICP-OES)

158

Calcium, potassium, magnesium, sodium and phosphorus concentrations were determined by

159

optical emission spectroscopy with inductively coupled plasma as atomisation and excitation

160

source (ICP-OES Agilent 5110 SVDV Agilent Technologies, Victoria, Australia), using the

161

following wavelengths: 393.366; 396.847; 422.673 (Ca), 766.491 (K), 279.553; 280.270;

162

285.213 (Mg), 588.995; 589.592 (Na), 177.434; 178.222; 213.618; 214.914 (P). The analyses for

163

all ions were carried out in axial and/or radial view. The samples for the analysis were ashed,

164

dissolved in 1 mL 25% v/v HNO3, diluted with ultrapure water to the volume of 50 mL and

165

filtered through 0.22 µm PVDF syringe filters.

166

2.4.8 Lactic acid content

167

Lactic acid concentration in liquid whey and KCl solutions was determined through high-

168

performance liquid chromatography (HPLC) with a Waters chromatograph (Waters Corp.,

169

Milford, USA), equipped with a Hitachi differential refractometer detector L-7490 (Foster City,

170

California, USA), a 600E controller, a column oven, and a cooled 717Plus autosampler. An

171

ICSep ICE-ION-300 column (Transgenomic, Omaha, USA) was used with 8.5 mM of H2SO4

172

(180 µL H2SO4 per l) as the mobile phase at a flow rate of 0.4 mL/min. The column temperature

173

was kept constant at 40 °C. Samples were diluted with ultrapure water and filtered with nylon

174

CHROMSPEC Syringe Filter (Chromatographic Specialties, Brockville, ON, Canada, pore size

175

of 0.45 µm) before injection (15 µL). A mixture of lactose anhydrous (PHR1025) and L-(+)-

176

lactic acid and acetic acid (Sigma-Aldrich) was used as an external standard to perform

177

quantifications. The run time was 45 min.

178

2.4.9 Protein content

179

Protein content in whey powder was measured by Dumas method using FP-428 analyzer (LECO

180

Corp., Saint Joseph, USA). The ethylenediaminetetraacetic acid (EDTA) was used as the

181

calibration standard for nitrogen analysis. Conversion coefficient to calculate the protein content

182

was 6.25.

183

2.4.10 Membrane thickness

184

The thickness of membranes was measured with digital micrometer CO 030025 (Marathon

185

Management Company, Richmond Hill, Canada). The average of six measurements at different

186

points on each membrane was calculated as the thickness value.

187

2.4.11 Membrane conductivity

188

The electrical conductivity of membranes was measured with a specially designed clip cell

189

(Laboratoire des Matériaux Echangeurs d’Ions, Créteil, France). Conductivity κ (mS/cm) was

190

calculated as follows:

191

κ=

0.1 l ,  1 1  A  −  G  m+s Gs 

192

l is membrane thickness (cm), Gm+s is conductance of a membrane in 0.5 M NaCl solution (mS),

193

Gs is conductance of 0.5 M NaCl solution (mS), and A is the electrode area (1 cm2) (Rozoy et al.,

194

2015).

195

2.5 Statistical analyses

196

Data were subjected to one-way or multiple way analyses using Statistical Analysis System 9.4

197

software (SAS Institute Inc., Cary, USA). Waller-Duncan’s multiple range tests (significance

198

level p=0.05) were used to determine statistical differences between conditions.

199 200

3. Results

201

3.1 Electrodialysis and solutions properties

202

3.1.1 pH of solutions

203

The main parameter of acid whey neutralization process, pH of whey and KCl solution showed

204

different evolutions (Fig. 2). Due to a lower number of membranes in cell configuration 2, the

205

cell resistance was significantly lower, and whey neutralization progresses nearly two times

206

faster. An exponential pattern of whey pH rise suggests a loss in whey buffer capacity during

207

EDBM mainly due to demineralization. pH of KCl solution decreased rapidly at the beginning of

208

the process as the H+ electrogeneration progresses. However, pH of the KCl solution reached a

209

plateau afterwards; the electrogenerated H+ ions possibly started leaking from the KCl

210

compartment through the AEM because of a critical concentration gradient (Fig. 3). pH values of

211

the streams contacting BPM can be quite low (for KCl solution) or high (for whey) after exiting

212

the cell, before the stream is mixed with the bulk solution in respective containers. The map

213

(Fig. 3) does not account for the possibility of water splitting at the ion-exchange membrane due

214

to concentration polarization.

215

3.1.2 Electrical conductivity of solutions

216

Electrical conductivity of whey is influenced by two competing phenomena: desalination and

217

alkalinization. Both tested cell configurations allowed demineralization of acid whey stream due

218

to anion migration, which diminished the conductivity of solution. On the other hand, the

219

electrogenerated hydroxide ions also contributed to the conductivity of whey. As follows from

220

Fig. 4, conductivity of whey slightly decreased after a short initial delay.

221

For KCl solution, electrically-driven ion migration and electrogeneration act synergistically;

222

therefore, electric conductivity of KCl increases drastically during EDBM. Difference in

223

conductivity increase for both cell configurations results in different cell resistance values; the

224

impact of H+ electrogeneration, as well as alkalinization, is much higher for the second cell

225

configuration.

226

3.1.3 Global system resistance and electric current

227

Global resistance of the cells did not show a steep increase in the end of the process (Fig. 5),

228

which suggests that the possible membrane fouling slightly contributed to the resistance of the

229

system. Initial cell resistance was relatively high, as the conductivity of KCl solution was too

230

low to conduct current as good as whey compartments; rapid ions concentration rise in KCl

231

solution promoted increase in the current through ED cell and resulted in a decrease of system

232

resistance. Expectedly, the second cell configuration showed slightly lower cell resistance due to

233

lower number of membranes and compartments. To calculate the resistance of ED cell, we used

234

measured values of electric current through the ED cell shown in the Fig. 6. 3.1.4 Energy consumption

235 236

It is clear that the efficiency of whey alkalinization was higher for the second cell configuration,

237

as the pH adjustment required less charge to be transported in this case; however, it is possible to

238

estimate EDBM economic efficiency in terms of energy consumption. Specific energy

239

consumption of EDBM was 27.7 ± 4.0 and 21.0 ± 1.3 W h kg–1 for cell configurations 1 and 2,

240

respectively. However, whey demineralization rate after treatment using cell configuration 1 was

241

higher; thus, a certain part of consumed energy was applied to extra demineralization. 3.1.5 Number of electrogenerated ions

242 243

The calculated amounts of electrogenerated OH– ions were 37.6 ± 5.4 and 56.9 ± 0.3 mmol l–1 h–

244

1

245

2 showed higher electrogeneration rate; this is in alignment with the recorded evolution of

246

conductivity KCl solution. The alkalinization rate of whey also corroborates the high efficiency

247

of cell configuration 2.

for cell configurations 1 and 2, respectively. According to these calculations, cell configuration

248

3.2 Analyses of whey

249

3.2.1 Ash content

250

Both cell configurations provided desalination of the acid whey compartment due to anions

251

migration to the KCl solution. Ash content in whey samples was measured to estimate and

252

compare desalination rates of the two cell configurations (Fig. 7). The final demineralization

253

rates were 34.0 ± 6.4% and 24.3 ± 5.6% for cell configurations 1 and 2, respectively. Moisture

254

content in lyophilized powders was determined in order to calculate whey demineralization rates

255

precisely. The change in the content of other dry matter components throughout EDBM was not

256

considered.

257

3.2.2 Mineral composition

258

ICP-OES of whey samples was conducted to track the changes in concentration of specific

259

elements after EDBM treatment and correlate these changes with those observed prior to the

260

processing. As shown in Fig. 8, there was a significant loss in calcium, magnesium and

261

potassium concentrations in treated acid whey. Changes in cationic concentrations are well

262

explainable by the features of cell configurations (Fig. 1). Cell configuration 1 allows cationic

263

exchange between diluate and electrode solution, i.e. sodium, potassium, calcium and

264

magnesium concentrations are free to equilibrate through CEMs. Sodium gain in acid whey

265

stream resulted from Na+ ions migration from electrode solution (sodium nitrate of relatively

266

high concentration). Vice versa, K⁺ , Ca²⁺ and Mg²⁺ migrated from acid whey stream to

267

electrode solution. In case of cell configuration 2, cationic migration from electrode solution was

268

prevented by AEMs adjacent to the electrodes. Nevertheless, potassium, calcium and magnesium

269

concentrations declined, which indicates possible leakage of the cations to the KCl compartment.

270

However, the decrease in Ca is comparable for both cell configurations and may be referred to

271

such phenomena as membrane scaling (3.2.4) and formation of colloidal calcium phosphate

272

species in the bulk solution (Chandrapala et al., 2015).

273

3.2.3 Lactic acid content

274

Data obtained from HPLC of acid whey and KCl solution samples are shown in Fig. 9. The

275

initial content of lactic acid in whey showed slightly accelerating decrease throughout the EDBM

276

run for both cell configurations. Total lactic acid removal was similar and resulted in 26 and 24%

277

lactic acid reduction for cell configurations 1 and 2, respectively, regardless of EDBM duration.

278

Surprisingly, pronounced migration of lactate to KCl solution was only observed in EDBM run

279

with cell configuration 1. However, traces of lactic acid were detected in a final KCl solution in

280

case of cell configuration 2 as well.

281

3.2.4 Protein content

282

A membrane fouling was observed after EDBM on the anion-exchange side of BPM, adjacent to

283

the diluate compartment (Fig. 10). It was supposed that there was an undesirable influence of

284

EDBM on the final protein content in processed whey. Indeed, the protein fraction of whey

285

significantly contributes to the value of a final product (Božanić et al., 2014; Macwan et al.,

286

2016). Therefore, the protein content in the processed whey was defined by Dumas method and

287

compared with that of initial whey (Fig. 11). The change in protein content of whey after EDBM

288

treatment was around 5% for both cell configurations applied; thus, protein loss due to fouling

289

did not lead to dramatic decrease in the nutritional value of processed whey. Also, there was no

290

significant impact of cell configuration type on the protein loss during EDBM.

291

Protein precipitation and its subsequent contribution to membrane fouling resulting from EDBM

292

of acid whey was studied in more detail. The data obtained can be found in Supplementary

293

materials for present paper (For the schematic description of experimental protocol see Fig. A in

294

Supplementary materials section). EDBM of centrifuged acid whey using cell configuration 2 led

295

to the protein precipitation (around 10% of initial protein content in feed), whereas only 7%

296

protein was found in the dry matter of collected membrane fouling.

297

3.3 Membranes analyses

298

Thickness of each membrane was measured prior to EDBM and after the treatment to

299

characterize membrane scaling. The results of measurements are presented in Fig. 12. Thickness

300

of membrane samples after EDBM was not significantly different from initial values, revealing

301

no build-up of membrane scaling due to EDBM processing.

302

The electrical conductivity of studied membranes decreased averagely by 10–30% after EDBM

303

(Fig. 13). This decrease is not severe as compared with 30–80% loss in conductivity after the

304

process of snow crab by-product peptide hydrolysate fractionation reported in (Suwal et al.,

305

2016). The decrease in conductivity could be caused by the deposition of sparingly soluble

306

calcium and magnesium salts in the membranes. However, elemental profiling revealed a

307

noticeable increase in calcium content only for CEMs, while the extent of conductivity reduction

308

was similar for all tested membranes (Fig. 15). Similar decrease in membrane conductivity was

309

observed in recent work of Dufton et al. (Dufton et al., 2018). The authors attributed slight

310

change in CEMs conductivity to the substitution of relatively mobile Na+ by Ca2+ from whey in

311

pristine membranes; it is probably correct for the AEMs as well, where Cl– could be replaced

312

with lactates or phosphates. In this case, the residual phosphates and lactated remained in AEM

313

after soaking in NaCl could lower membrane conductivity. The ash content was measured in

314

membrane samples to estimate possible mineral deposition. The data on the change in membrane

315

ash content after EDBM is displayed in Fig. 14. Ash content in AEMs appeared to be negligible.

316

Only BPM samples after EDBM using cell configuration 2 showed a significant change in ash

317

content as compared to the original values.

318

Another method applied in order to characterize membrane mineral fouling was ICP-OES,

319

capable to determine the content of major scaling elements, Mg and Ca (Mikhaylin and Bazinet,

320

2016) (Fig. 15). Data obtained by means of ICP-OES indicated an increase in calcium content

321

for CEM after EDBM treatment. However, this contribution to the mineral composition of CEM

322

was compensated by the loss of Na. Thus, it was difficult to detect deposition of calcium species

323

by means of ash content analysis. Presumably, the observed decrease of Na concentration both in

324

CEM and BPM was due to substitution of originally present Na+ ions by H+ on membrane

325

sulfonic groups. The increase in calcium concentration and loss of sodium were also

326

characteristic of BPM; both processes were more intensive in case of cell configuration 2, which

327

is probably relating to higher current values during the process. AEMs did not show any

328

noticeable change in content of Ca, Mg, K and Na.

329 330

4. Discussion

331

4.1 Electrodialysis

332

The resistance of the three-membrane cell configuration 1 was higher than that of four-

333

membrane cell configuration 2 (Fig. 5), while the applied voltage was equal for both cells. Thus,

334

many differences in parameters of EDBM were dependent on the fact that the tested cell

335

configurations included different number of membranes. Current density varied from 3.1 to 12.1

336

A cm–2 and 4.1 to 18.1 A cm–2 for cell configurations 1 and 2, respectively. Process energy

337

consumption, on the contrary, was around 25% lower for cell configuration 2. Finally, the

338

estimated number of electrogenerated ions was 1.5 times higher for cell configuration 2. These

339

data hint at the relative efficiency of latter. Indeed, cell configuration 2 provided significantly

340

higher alkalinization rate. It took almost twice longer to raise pH to 6.5 using cell configuration 1

341

(Fig. 2). Prolonged duration of EDBM with cell configuration 1 resulted in a higher whey

342

demineralization rate (Fig. 7), but the removal rate of lactate was similar for both cell

343

configurations (Fig. 9).

344

The equilibrium between lactic acid and lactate is susceptible to pH changes. it is shifted to the

345

dissociated form in alkaline media:

346 347

Neutral molecules of lactic acid dissociate to lactate and H⁺ ions that are removable by means

348

of electrodialysis. Thus, alkalinization of whey is capable to enhance the removal of lactate. pH

349

of whey could be one of the driving factors for the observed acceleration in lactate removal rate

350

(Fig. 9).

351

The lactic acid was accumulating in KCl solution during EDBM run with cell configuration 1.

352

However, no lactate was found in KCl solution samples throughout EDBM with cell

353

configuration 2: final lactate concentration in KCl solution was as low as 70 mg/L, and zero

354

lactate content was measured in the preceding samples. This difference in lactate migration could

355

be explained by the difference between the two tested ED cells (Fig. 1). Indeed, cell

356

configuration 1 allows direct migration of negatively charged species from whey to the KCl

357

solution, while electrode solution is isolated from anions of whey by the CEMs. In cell

358

configuration 1 anionic species initially migrate to the anolyte compartment; afterwards, anolyte

359

is mixed with catholyte and recycles, so that the lactate is eventually capable to migrate from

360

catholyte compartment to the KCl solution. However, electrode solution contains a high

361

concentration of highly mobile nitrate ions, making up the majority of the current through the

362

AEM between catholyte and KCl solution. Consequently, a certain time was required for lactate

363

to accumulate in the electrode solution to contribute to the ion transport to the KCl solution.

364

Conductivity change in whey during EDBM was similar for both tested cell configurations. The

365

changes in conductivity of the KCl solutions were, however, substantially different. A moderate

366

increase in the conductivity of KCl solution was observed throughout EDBM runs using cell

367

configuration 1 (Fig. 4). In case of cell configuration 2 the increase in the conductivity of KCl

368

solution was drastic; the value greater than 30 mS/cm was reached by the end of EDBM. The

369

conductivity increase in the KCl stream was due to the migration of negatively charged species

370

through the AEM. The KCl compartment was supplied with anions by acid whey in cell

371

configuration 1 and by electrode solution in cell configuration 2. It appears that the nitrate-rich

372

electrode solution provided much more abundant anionic migration to the KCl stream. In its turn,

373

whey contained lower concentrations of chlorides and poor dissociating phosphates and lactates

374

that were unable to increase the conductivity of KCl stream that high.

375

4.2 Bulk precipitation and membrane fouling

376

Protein precipitation in whey during EDBM seems to be a result of non-electrostatic interactions

377

between protein molecules. The isoelectric point of major whey proteins, β-lactoglobulin and

378

α-lactalbumin, are around pH 5.2–5.4 and 4.2–4.8, respectively (McSweeney and Fox, 2013).

379

The fact that the precipitation takes place on the surface of BPM suggests that the specific

380

conditions here promote fouling formation. This suggestion is in accordance with (Chandrapala

381

et al., 2015); the authors reported a slight decrease in soluble whey proteins concentration after

382

the increase in acid whey pH (3.0 to 10.5). Also, the precipitation was assessed at different

383

temperatures (15, 25, 40, 90 °C) with a peak of protein loss at 90 °C. Interestingly, surface

384

hydrophobicity of proteins is of maximum value at 40 °C for each pH value and rises with pH

385

increase. These data stress the role of hydrophobic interactions on protein precipitation process.

386

Thus, it is possible that both chemical conditions and high temperature promoted protein

387

precipitation in the acid whey compartment of ED cell during EDBM. Indeed, the temperature of

388

bulk whey reached 38 °C during EDBM process (Fig. C, Supplementary materials) and it was

389

even higher in the diluate compartment of ED cell.

390

It was also found that the raw whey used in present study contained a considerable amount of

391

protein precipitate (22.6 ± 1.0% of total protein amount); presumably, this substance included

392

mainly thermally denatured whey protein and was likely to contribute to the fouling. The latter

393

hypothesis is supported by the fact that the protein content in raw acid whey after EDBM

394

changed from 8.10 ± 0.42% to 7.67 ± 0.32%. Protein content in centrifuged acid whey was 6.29

395

± 0.28% and 6.63 ± 0.25% before and after EDBM, respectively, i.e. no protein loss was

396

revealed after EDBM in case of preliminary removal of initially present proteinaceous fraction

397

from whey (Table A, Supplementary materials).

398

As the protein content in both the observed membrane fouling and bulk precipitate made up

399

around 10% of its dry mass, the majority of the fouling matter and precipitate is considered to be

400

mineral. Mineral fouling is encountered in various dairy processing operations, e.g. evaporation

401

(Paterson, 2017; Tanguy et al., 2016), ultrafiltration (Heng and Glatz, 1991; PATOCKA and

402

JELEN, 1987) and nanofiltration (Chandrapala et al., 2016b; Rice et al., 2009). Calcium

403

phosphate species are reported to be the main constituent of mineral deposits in the systems

404

processing milk, whey and respective ultrafiltration permeates. The inverse solubility of calcium

405

phosphate along with its poor solubility in basic media (Elliot, 1994) corroborates mineral

406

precipitation on the diluate side of BPM during EDBM of whey. Analogically, alkalinization of

407

acid whey stream would also lead to precipitation of calcium salts in the bulk solution. The

408

analyses of membranes thickness (Fig. 12) and ash content (Fig. 14) gave no evidence of scaling.

409

On the other hand, conductivity of membranes exhibited a moderate decrease after EDBM

410

(Fig. 13); the elemental analysis of membrane samples (Fig. 15) revealed a pronounced calcium

411

deposition in CEM. Calcium content in BPM after EDBM increased slightly; but no scaling was

412

visually observed on the membranes after EDBM treatments in the different configurations.

413

A straightforward acid whey alkalinization by bringing whey stream into contact with an anion-

414

exchange BPM surface could be improved, e.g., by introducing a buffer compartment for basic

415

solution between BPM and acid whey compartment in order to minimize membrane fouling.

416

However, this would result in a further complication of ED stack scheme.

417 418

5. Conclusions

419

The two tested cell configurations were approximately equally efficient for acid whey

420

alkalinization. Cell configuration 2 was favorable in terms of energy consumption. However, the

421

final demineralization rate of whey treated using cell configuration 2 was lower due to the

422

impossibility of selective removal of cations from whey. Both cell configurations allow removal

423

of negatively charged species; the removal rate of lactic acid was around 25%. Thus, the EDBM

424

is feasible for improving organoleptic properties of acid whey, while lactic acid removal rate was

425

low as compared to 44% deacidification rate achieved in (Dufton et al., 2018) and requires

426

improvement to provide better processability of acid whey.

427

It was found that the observed membrane fouling does not affect the total amount of proteins in

428

whey substantially. However, EDBM still induces a precipitation of whey proteins; this

429

phenomenon may influence technological and nutritional properties of product negatively.

430

Preliminary clarification of whey is capable to intensify EDBM process due to decrease in whey

431

buffer capacity and global resistance of the system. The fact that the protein precipitation and

432

fouling appear after the removal of residual casein fines and denatured whey protein fraction

433

indicates that the whey proteins do participate in the formation of the membrane fouling. Dumas

434

analysis of membrane fouling displayed minor protein content; thus, mineral fraction is likely to

435

be dominant in the membrane fouling.

436 437

6. Acknowledgements

438

The Natural Sciences and Engineering Research Council of Canada (NSERC) financial support

439

is acknowledged. This work was supported by the NSERC Industrial Research Chair on

440

ElectroMembrane processes aiming the ecoefficiency improvement of biofood production lines

441

(Grant IRCPJ 492889-15 to Laurent Bazinet) and the NSERC Discovery Grants Program (Grant

442

SD RGPIN-2018-04128 to Laurent Bazinet). The authors thank Jacinthe Thibodeau and Diane

443

Gagnon, research professionals at Université Laval, for their kind and patient aid in the operation

444

of laboratory equipment. Also, the authors thank Alain Brousseau (Laval University) as well as

445

Véronique Richard (Laval University and INAF) for their respective involvement in ICP and

446

HPLC analyses and Pascal Lavoie (Laval University) for the aid in lyophilization of the samples.

447 448

7. References

449

Bazinet, L., Ippersiel, D., Gendron, C., Beaudry, J., Mahdavi, B., Amiot, J., Lamarche, F., 2000.

450

Cationic balance in skim milk during bipolar membrane electroacidification. J. Memb. Sci.

451

173, 201–209. https://doi.org/10.1016/S0376-7388(00)00373-2

452

Bédas, M., Tanguy, G., Dolivet, A., Méjean, S., Gaucheron, F., Garric, G., Senard, G., Jeantet,

453

R., Schuck, P., 2017a. Nanofiltration of lactic acid whey prior to spray drying: Scaling up to

454

a semi-industrial scale. LWT - Food Sci. Technol. 79, 355–360.

455

https://doi.org/10.1016/j.lwt.2017.01.061

456

Bédas, M., Tanguy, G., Dolivet, A., Méjean, S., Gaucheron, F., Garric, G., Senard, G., Jeantet,

457

R., Schuck, P., 2017b. Nanofiltration of lactic acid whey prior to spray drying: Scaling up to

458

a semi-industrial scale. LWT - Food Sci. Technol. 79, 355–360.

459

https://doi.org/10.1016/j.lwt.2017.01.061

460 461

Božanić, R., Barukčić, I., Lisak, K., 2014. Possibilities of whey utilisation. J. Nutr. Food Sci. 2, 1–7.

462

Chandrapala, J., Chen, G.Q., Kezia, K., Bowman, E.G., Vasiljevic, T., Kentish, S.E., 2016a.

463

Removal of lactate from acid whey using nanofiltration. J. Food Eng. 177, 59–64.

464

https://doi.org/10.1016/j.jfoodeng.2015.12.019

465

Chandrapala, J., Duke, M.C., Gray, S.R., Weeks, M., Palmer, M., Vasiljevic, T., 2017. Strategies

466

for maximizing removal of lactic acid from acid whey – Addressing the un-processability

467

issue. Sep. Purif. Technol. 172, 489–497. https://doi.org/10.1016/j.seppur.2016.09.004

468

Chandrapala, J., Duke, M.C., Gray, S.R., Weeks, M., Palmer, M., Vasiljevic, T., 2016b.

469

Nanofiltration and nanodiafiltration of acid whey as a function of pH and temperature. Sep.

470

Purif. Technol. 160, 18–27. https://doi.org/10.1016/j.seppur.2015.12.046

471

Chandrapala, J., Duke, M.C., Gray, S.R., Zisu, B., Weeks, M., Palmer, M., Vasiljevic, T., 2015.

472

Properties of acid whey as a function of pH and temperature. J. Dairy Sci. 98, 4352–4363.

473

https://doi.org/10.3168/jds.2015-9435

474

Chandrapala, J., Vasiljevic, T., 2017. Properties of spray dried lactose powders influenced by

475

presence of lactic acid and calcium. J. Food Eng. 198, 63–71.

476

https://doi.org/10.1016/j.jfoodeng.2016.11.017

477

Chandrapala, J., Wijayasinghe, R., Vasiljevic, T., 2016c. Lactose crystallization as affected by

478

presence of lactic acid and calcium in model lactose systems. J. Food Eng. 178, 181–189.

479

https://doi.org/10.1016/j.jfoodeng.2016.01.019

480

Chen, G.Q., Eschbach, F.I.I., Weeks, M., Gras, S.L., Kentish, S.E., 2016. Removal of lactic acid

481

from acid whey using electrodialysis. Sep. Purif. Technol. 158, 230–237.

482

https://doi.org/10.1016/j.seppur.2015.12.016

483

Dufton, G., Mikhaylin, S., Gaaloul, S., Bazinet, L., 2018. How electrodialysis configuration

484

influences acid whey deacidification and membrane scaling. J. Dairy Sci. 1–18.

485

https://doi.org/10.3168/jds.2018-14639

486

Duke, M., Vasiljevic, T., 2015. Whey Processing: Overview and Role of Membranes, in:

487

Encyclopedia of Membranes. Springer Berlin Heidelberg, pp. 1–4.

488

https://doi.org/10.1007/978-3-642-40872-4_2063-1

489 490 491 492 493 494

Elliot, J.C., 1994. Structure and Chemistry of the Apatites and Other Calcium Orthophosphates, Volume 18, 1st ed. https://doi.org/10.1016/B978-0-444-88534-0.50001-1 Heng, M.H., Glatz, C.E., 1991. Chemical Pretreatments and Fouling in Acid Cheese Whey Ultrafiltration. J. Dairy Sci. 74, 11–19. https://doi.org/10.3168/jds.S0022-0302(91)78138-1 Kilara, A., 2016. Whey and Whey Products, in: Chandan, R.C., Kilara, A., Shah, N.P. (Eds.), Dairy Processing and Quality Assurance. John Wiley & Sons, Ltd., pp. 349–366.

495 496

https://doi.org/10.1002/9781118810279.ch15 Królczyk, J.B., Dawidziuk, T., Janiszewska-Turak, E., Sołowiej, B., 2016. Use of Whey and

497

Whey Preparations in the Food Industry - A Review. Polish J. Food Nutr. Sci. 66, 157–165.

498

https://doi.org/10.1515/pjfns-2015-0052

499

Lin Teng Shee, F., Bazinet, L., 2009. Cationic balance and current efficiency of a three-

500

compartment bipolar membrane electrodialysis system during the preparation of chitosan

501

oligomers. J. Memb. Sci. 341, 46–50. https://doi.org/10.1016/j.memsci.2009.05.028

502 503 504

Macwan, S.R., Dabhi, B.K., Parmar, S.C., Aparnathi, K.D., 2016. Whey and its Utilization. Int.J.Curr.Microbiol.App.Sci 5, 134–155. https://doi.org/10.20546/ijcmas.2016.508.016 McSweeney, P.L.H., Fox, P.F. (Eds.), 2013. Advanced dairy chemistry: Volume 1A: Proteins:

505

Basic aspects, 4th edition, 4th ed, Advanced Dairy Chemistry: Volume 1A: Proteins: Basic

506

Aspects, 4th Edition. Springer. https://doi.org/10.1007/978-1-4614-4714-6

507

Merkel, A., Ashrafi, A.M., Ečer, J., 2018. Bipolar membrane electrodialysis assisted pH

508

correction of milk whey. J. Memb. Sci. 555, 185–196.

509

https://doi.org/10.1016/j.memsci.2018.03.035

510

Mier, M.P., Ibañez, R., Ortiz, I., 2008. Influence of process variables on the production of bovine

511

milk casein by electrodialysis with bipolar membranes. Biochem. Eng. J. 40, 304–311.

512

https://doi.org/10.1016/j.bej.2007.12.023

513

Mikhaylin, S., Bazinet, L., 2016. Fouling on ion-exchange membranes: Classification,

514

characterization and strategies of prevention and control. Adv. Colloid Interface Sci. 229,

515

34–56. https://doi.org/10.1016/j.cis.2015.12.006

516

Nishanthi, M., Chandrapala, J., Vasiljevic, T., 2017a. Compositional and structural properties of

517

whey proteins of sweet, acid and salty whey concentrates and their respective spray dried

518

powders. Int. Dairy J. https://doi.org/10.1016/j.idairyj.2017.01.002

519 520

Nishanthi, M., Vasiljevic, T., Chandrapala, J., 2017b. Properties of whey proteins obtained from different whey streams. Int. Dairy J. 66, 76–83.

521

https://doi.org/10.1016/j.idairyj.2016.11.009

522

Panesar, P.S., Kennedy, J.F., Gandhi, D.N., Bunko, K., 2007. Bioutilisation of whey for lactic

523

acid production. Food Chem. 105, 1–14. https://doi.org/10.1016/j.foodchem.2007.03.035

524

Paterson, A.H.J., 2017. Lactose processing: From fundamental understanding to industrial

525

application. Int. Dairy J. 67, 80–90. https://doi.org/10.1016/j.idairyj.2016.07.018

526

PATOCKA, J., JELEN, P., 1987. Calcium Chelation and Other Pretreatments for Flux

527

Improvement in Ultrafiltration of Cottage Cheese Whey. J. Food Sci. 52, 1241–1244.

528

https://doi.org/10.1111/j.1365-2621.1987.tb14052.x

529

Rice, G., Barber, A., O’Connor, A., Stevens, G., Kentish, S., 2009. Fouling of NF membranes by

530

dairy ultrafiltration permeates. J. Memb. Sci. 330, 117–126.

531

https://doi.org/10.1016/j.memsci.2008.12.048

532

Rozoy, E., Boudesocque, L., Bazinet, L., 2015. Deacidification of cranberry juice by

533

electrodialysis with bipolar membranes. J. Agric. Food Chem. 63, 642–651.

534

https://doi.org/10.1021/jf502824f

535

Saffari, M., Langrish, T., 2014. Effect of lactic acid in-process crystallization of lactose/protein

536

powders during spray drying. J. Food Eng. 137, 88–94.

537

https://doi.org/10.1016/j.jfoodeng.2014.04.002

538 539

Salaün, F., Mietton, B., Gaucheron, F., 2005. Buffering capacity of dairy products. Int. Dairy J. 15, 95–109. https://doi.org/10.1016/j.idairyj.2004.06.007

540

Suwal, S., Amiot, J., Beaulieu, L., Bazinet, L., 2016. Effect of pulsed electric field and polarity

541

reversal on peptide/amino acid migration, selectivity and fouling mitigation. J. Memb. Sci.

542

510, 405–416. https://doi.org/10.1016/j.memsci.2016.03.010

543

Tanguy, G., Siddique, F., Beaucher, E., Santellani, A.C., Schuck, P., Gaucheron, F., 2016.

544

Calcium phosphate precipitation during concentration by vacuum evaporation of milk

545

ultrafiltrate and microfiltrate. LWT - Food Sci. Technol. 69, 554–562.

546

https://doi.org/10.1016/j.lwt.2016.02.023

547

Tronc, J.-S., Lamarche, F., Makhlouf, J., 1997. Enzymatic Browning Inhibition in Cloudy Apple

548

Juice by Electrodialysis. J. Food Sci. 62, 75–78. https://doi.org/10.1111/j.1365-

549

2621.1997.tb04371.x

550 551

Zadow, J.G., 1992. Whey and Lactose Processing. https://doi.org/10.1007/978-94-011-2894-0

552

8. Supplementary materials

553

To characterize protein distribution between colloidal and liquid phases of whey, a

554

complementary electrodialysis experiment was conducted. Prior to EDBM, the remains of casein

555

fraction were eliminated from raw acid whey by centrifugation (5000 rpm, 15 min, 4 °C). The

556

resulted supernatant was used as diluate solution in EDBM (ED parameters as in 2.2–2.3, cell

557

configuration 2). Cell configuration 2 was selected as the most efficient in terms of whey

558

alkalinization yet producing a large amount of precipitate in whey. After EDBM, the alkalinized

559

whey was centrifuged (5000 rpm, 15 min, 4 °C) in order to separate suspended whey protein

560

precipitate. Raw whey, alkalinized whey and yield of two centrifugations (supernatants and

561

precipitates) were sampled to determine protein content. The samples were weighed and then

562

freeze-dried to obtain powders. The algorithm of whey treatment was realized according to the

563

scheme shown in Fig. A.

564

It is clear that the removal of initially present precipitate from whey resulted in the increase in

565

alkalinization rate (Fig. B). It was assumed that the majority of the eliminated fraction was of

566

protein nature, including remains of casein fines and mainly a portion of whey proteins

567

(thermally denatured) precipitated in the freezing-defrostation cycle. The increase in

568

alkalinization rate is probably determined by the change in the buffer capacity of whey after

569

partial proteins removal by centrifugation. High-molecular caseins and whey proteins grant a

570

large amount of sites for H+ deposition even in denatured state (Salaün et al., 2005); as soon as

571

this colloid fraction is removed by centrifugation, whey buffer capacity lowers, and

572

alkalinization is accelerated.

573

Also, the minor increase in global cell resistance was observed in the case of EDBM of raw acid

574

whey, while no noticeable increase in resistance was registered during EDBM of clarified whey

575

(Fig. B).

576

Table A presents data on analyses of protein precipitation during the treatment of acid whey.

577

Protein content in whey, alkalinized whey and their fractions is given. The contribution of a

578

certain fraction to the total protein amount in whey was calculated using the following

579

expression:

580

p=

cpm C pM

⋅ 100 %,

581

cp is the protein concentration (% w/w) in a spray-dried sample of whey fraction (supernatant or

582

precipitate); Cp is the protein concentration (% w/w) in a spray-dried whey sample prior to

583

fractionation; m is the mass of a spray-dried sample of whey fraction; M is the mass of a spray-

584

dried whey sample prior to fractionation.

585

As follows from the protein analysis, there was no loss of protein after EDBM of centrifuged

586

whey, while after EDBM of raw whey using the same ED cell configuration the loss was of

587

5.3 ± 9.1% (Fig. 11). However, appearance of the fouled bipolar membranes surface after raw

588

whey EDBM and centrifuged whey EDBM was identical.

589

It should be noted that the protein content in precipitates and membrane fouling were quite low

590

(12.90 ± 1.98% in the precipitate after EDBM, 7.22 ± 0.09% in membrane fouling), i.e. proteins

591

appeared to be a minor component in the precipitates.

592

Table 1. Composition and physicochemical characteristics of the raw acid whey. Unit

Acid whey

Total solids

g/L

59.8 ± 4.2

Total protein

g/L

6.5 ± 0.7

Lactose

g/L

41.2 ± 0.9

Minerals

g/L

5.1 ± 1.1

P

g/L

0.55 ± 0.01

Ca

g/L

0.86 ± 0.02

K

g/L

1.26 ± 0.05

Mg

g/L

0.09 ± 0.00

Na

g/L

0.39 ± 0.03

Lactate

g/L

7.00 ± 0.14

Ratio

0.17

Lactate/Lactose

4.4

pH Conductivity

mS/cm

7.05 ± 0.24

593 594

Table A. Protein content in fractions of acid whey EDBM processing (cell configuration 2) Protein content

Percentage in total protein

in dried sample (%)

amount, (%)

7.15 ± 0.08

100

Acid whey supernatant

6.29 ± 0.28

86.4 ± 4.1

Acid whey precipitate

38.22 ± 1.29

22.6 ± 1.0

6.63 ± 0.25

100

6.39 ± 0.27

94.3 ± 3.4

12.90 ± 1.98

9.7 ± 1.1

7.22 ± 0.09

N/D

Sample Raw acid whey

Alkalinized whey Alkalinized whey supernatant Alkalinized whey precipitate

Membrane fouling 595 596

597

Fig. 1. Cell configurations with flows of acid whey, KCl solution and NaNO3 electrode solution.

598

C+ and A– indicate positively and negatively charged species, respectively.

599 600 601

602 603

Fig. 2. Evolution of pH in acid whey and KCl solution during EDBM process.

604 605

Fig. 3 Suggested pH map resulted from electrogeneration of H+ and OH– ions in cell

606

compartments adjacent to BPM (end of EDBM processing). Dashed lines indicate potential

607

leakage of H⁺ through AEMs.

608 609 610

611 612 613

Fig. 4. Evolution of electrical conductivity in acid whey and KCl solution during EDBM.

614

Fig. 5. Evolution of the global system resistance during EDBM.

615 616 617

618 619 620

Fig. 6. Electric current through ED cells during EDBM.

621

Fig. 7. Ash content in acid whey powder and alkalinized powdered samples.

622 623 624

625 626 627

Fig. 8. Elemental composition of original acid whey and whey after EDBM treatment.

628

629 630 631

Fig. 9. Lactic acid concentration in acid whey and KCl solution after EDBM.

632

Fig. 10. Anion-exchange side of BPM (a) and diluate compartment spacer (b) before EDBM

633

(above) and after EDBM (below). Cell configuration 2.

634 635 636

637 638 639

Fig. 11 . Protein loss in whey after EDBM treatment.

640

Fig. 12. Influence of EDBM on membranes thickness. Here and further, for each group, values

641

marked with different letters are significantly different.

642 643 644

645 646 647

Fig. 13. Electrical conductivity of membrane samples before and after EDBM.

648

Fig. 14. Ash content in membrane samples before and after EDBM.

649 650 651

652

Fig. 15. Mineral content in ion-exchange membranes prior and after electrodialysis.

653 654

Fig. A. Fractionation and EDBM of acid whey.

655 656 657

Fig. B. Whey pH and cell resistance during EDBM of raw acid whey and centrifuged acid whey

658

(cell configuration 2).

659 660 661

662

663

Fig. C. Temperature of acid whey in EDBM process.

• • • •

Electrodialysis with bipolar membranes provided an increase in pH of whey up to 6.5 Lactic acid removal rate was around 25% and demineralization varied from 24 to 34% Fouling only affected the surface of bipolar membrane in contact with acid whey The fouling matter was mostly of mineral nature with a minor protein component

Conflict of Interest and Authorship Conformation Form We, the authors of the paper “Alkalinization of acid whey by means of electrodialysis with bipolar membranes and analysis of induced membrane fouling” Vitalii Kravtsova, Irina Kulikovaa, Sergey Mikhaylinb, c, Laurent Bazinetb, c confirm that

a

b

o

All authors have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.

o

This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue.

o

The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript

Chair of Applied Biotechnology, Institute of Life Sciences, North-Caucasus Federal University, 1 Pushkin St., Stavropol 355009, Russia

Institute of Nutrition and Functional Foods, Dairy Research Center, and Department of Food Sciences, Université Laval, Québec, QC, Canada G1V 0A6 c

Laboratoire de Transformation Alimentaire et Procédés ÉlectroMembranaires (Laboratory of Food Processing and ElectroMembrane Processes), Université Laval, Québec, QC, Canada G1V 0A6